If you're passing a clob variable to oracle stored procedure, you could:
<?php
$qry = 'begin my_sp(:largetext); end;';
$stmt = oci_parse($conn, $qry); //definition of $conn is not included here
$clob = oci_new_descriptor($conn, OCI_D_LOB);
oci_bind_by_name($stmt, ":largetext", $clob, -1, OCI_B_CLOB);
$clob->writetemporary($mylargedata);
oci_execute($stmt);
$clob->free();
oci_free_statement($stmt);
?>
Hopefully this will help!